The present invention relates in general to a tool for disassembling threaded fasteners. More particularly, the present invention relates to a tool for removing collars from threaded bolts, such as frangible fasteners used in the aerospace industry.
Frangible fasteners are used extensively in the aerospace industry due to their simplicity, consistently controlled pre-load torque and minimum size and weight. As illustrated in FIG. 1, the fastener basically consists of two parts: a threaded bolt and a threaded nut. The end of the bolt has a configured recess, typically hexagonal, so that an Allen wrench may be inserted to hold the bolt stationary while the nut is rotated. The nut, which is the key component, consists of an internally threaded locking collar which threads onto the bolt. The collar is joined by a grooved neck to a wrenching ring which shears from the collar when the applied torque exceeds a predetermined torsional loading (FIG. 2). The fasteners are applied with one of a variety of wrenching tools which engage the wrenching ring to apply rotational force to the threaded collar and twist the wrenching ring from the threaded collar when the predetermined torsional loading is exceeded. The break-off torque depends on the depth of the groove in the neck which can be selected to meet different torque requirements.
The collar is a relatively smooth surface of revolution, so that once installed it cannot be rotated by conventional wrenches. This design prevents the pre-selected torque from being inadvertently changed. This "tamper proof" feature eliminates torque inspection after installation.
These fasteners are very effective and are intended to be permanently installed. Sometimes, however, the fasteners need to be removed due to any number of reasons including assembly errors or the need to repair the structure. The threaded collar commonly has a cylindrical base which tapers into a smaller diameter cylindrical neck. The cylindrical portions of these collars are narrow and are difficult to grasp with conventional tools such as pliers, vice grip clamps, etc. Although there have been a variety of tools designed to remove these fasteners, many of these tools require a relatively large volume of access space around the collar for removal. However, complex aerospace structures often have such fasteners in locations where access is limited, which prevents the prior removal tools from being effectively utilized.
Other fastener removal tools are hand operated and must be held and operated simultaneously with both hands. They usually require some skill and increase the likelihood of errors and tool slips. The use of such tools for loosening or removing aerospace fasteners is considered undesireable as they can damage the surfaces of the assembled parts.
There have been devised removal tools using a clutch member threadedly received with a collet sleeve which are attachable to a hand or power driven rachet wrench. However, many of these tools are not suitable for use with corroded or otherwise fused fasteners since the grip of the collet fingers about the collar is limited. Other collet removal tools are complicated in design and structure.
Accordingly, there is a need for a fastener removal tool with increased gripping force. A fastener removing tool which can be used in small areas and which will not damage the surfaces of the assembled parts is also needed. Such a tool should be capable of being used in connection with power tools. Furthermore, what is needed is a fastener collar removal tool which is simple in design and structure. The present invention fulfills these needs and provides other related advantages.